In recent several years, more and more experts pay much attention to research and development on mechanical characteristic monitoring of a circuit breaker. The dynamic characteristics of a circuit breaker can reflect the running failure of the circuit breaker effectively. Therefore, the mechanical characteristic is considered as one of the most important features for a circuit breaker, and there is a requirement to monitor the mechanical characteristic of a circuit breaker.
Currently, mechanical characteristic monitoring of a circuit breaker is usually taken in an off-line environment by means of electronic sensors. The off-line environment may be a testing environment in which the circuit breaker is not electrically connected to the grid and thus would not subject the high voltage in the grid. The voltage for testing in the testing environment is relative low such that it would not impact the normal operation of the electronic sensors. However, since the circuit contact in off-line or testing environment does not subject the real high voltage, the monitored result can not accurately reflect the practical operation condition of the circuit breaker and thus can only act as a limited reference for studying the circuit breaker.
As the smart grid technology develops, there is a demand for intelligent circuit breakers which can on-line monitor the mechanical characteristic of the circuit breakers in their normal operation condition so as to support the functions of the smart grid. On-line monitoring can reflect the real operation condition of the circuit breaker, and thus is more useful in studying and controlling the circuit breaker.
One of the most important mechanical characteristics of a circuit breaker is the value of a contact force applied on a movable contact of the circuit breaker, especially during the closing period. This contact force is a basis for evaluating the other aspects of the mechanical characteristics of the circuit breaker, for example, the accurate closing and opening time point of the circuit breaker.
However, the current off-line monitoring method is not suitable for on-line monitoring the contact force. The high voltage of the grid in the on-line environment can easily damage the electronics for the off-line monitoring.
In addition, since the electrical closing and opening time point under the high voltage cannot represent the real mechanical closing and opening of the movable contact due to the breakdown conducting under high voltage, it is necessary to find the mechanical closing and opening time point of the movable contact in the operation condition of the circuit breaker so as to accurately monitoring the mechanical characters of the circuit breaker. However, it is difficult to directly monitor the accurate mechanical closing and opening time point of a circuit breaker under the high voltage.
Therefore, a method and device for on-line monitoring the mechanical characteristic of a circuit breaker, particularly for on-line monitoring the accurate contact force and the mechanical closing and opening time point is required.